On Iowa caucus night, only a fraction of voters typically participate. But among Republicans who attend, half are expected to be evangelical Christians, a group that helped propel Rick Santorum and Mike Huckabee to wins in the past. This cycle, there may be more division over whether to back mainstream Republicans or antiestablishment candidates. Judy Woodruff reports.

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JUDY WOODRUFF:

Almost every presidential election produces a bloc of voters who become a barometer for the outcome. On Friday, we looked at the role women voters of different ages will play in the Democratic caucuses here in Iowa.

Tonight, we look at a bloc of voters who will help foretell results on the Republican side.

In some ways, yesterday was just like any other Sunday at The Kathedral, an evangelical Christian church in Iowa's capital, Des Moines. Worshipers came together for a morning of prayer and enthusiastic song.

But when it came time for the sermon, Pastor Kenney Linhart left no doubt what he expects his congregates to do come Monday night.

KENNEY LINHART, Pastor, The Kathedral:

You want to see things change in Iowa? Do you want to see the glory of God come down to Iowa? Then you need to be involved in the political process.

JUDY WOODRUFF:

Only a fraction of Iowa voters typically go to caucus. But of those who attend on the Republican side, half are expected to be evangelical, or born-again Christians.

Iowa pollster Ann Selzer says, even as her latest survey shows Donald Trump leading among Republicans overall, Ted Cruz is ahead among evangelicals.

ANN SELZER, Selzer & Company: We see surprises all the time coming from the evangelical vote and that's why you have to look at Ted Cruz and his ability to organize that group as a potential surprise on caucus night.

JUDY WOODRUFF:

It was evangelicals who helped propel Mike Huckabee in 2008 and Rick Santorum four years ago to victory here. This year, not only are Huckabee and Santorum competing for those votes. So is a cluster of other Republicans.

Radio Iowa’s O. Kay Henderson:

O. KAY HENDERSON, Radio Iowa:

Nine months ago, Rand Paul was trying to lock in evangelical supporters. You have Ben Carson, who has really kept a core of support, and that comes from the states' evangelical churches.

You have Donald Trump, who has lined up an important endorsement from the president of Liberty University. And you have Ted Cruz, who has an effort to try to get a pastor in each precinct in Iowa.

JUDY WOODRUFF:

But the former chairman of the Iowa Republican Party, Matt Strawn, says the evangelical voters these candidates are after don't all have the same priorities.

MATT STRAWN, Former Chairman, Iowa Republican Party:

Take a look at Ted Cruz. Part of his coalition with people like Bob Vander Plaats, radio personality Steve Deace, very anti-establishment evangelical Christians, the type that want to blow up the system and start over, as opposed to maybe a larger group of Iowa Christian conservatives that would be the progeny of the Pat Robertson movement in the 1980s, Ralph Reed Christian Coalition, more pragmatic Christian conservatives who want to work within the system to shape it towards their beliefs.

And they're the folks that are your traditional caucus-goers that are still largely up for grabs.

JUDY WOODRUFF:

This latter group, Strawn says, have elected mainstream Republicans to office here for years. But that's exactly what Christian conservative leader Bob Vander Plaats says he doesn't want to see this time. He's backing Cruz.

BOB VANDER PLAATS, The Family Leader:

We trust conversions on the road to Damascus. We question conversions on the road to Des Moines. And so we take a look at, what were they doing before they ran for president? And so, at age 13, you know, he's memorizing the Constitution. He's deeply threaded with the Judeo-Christian world view.

SEN. TED CRUZ (R-TX), Republican Presidential Candidate:

What I want to ask of each of you is that you pray just a minute a day, that you say, father God, continue this awakening, continue this spirit of revival. Awaken the body of Christ.

JUDY WOODRUFF:

The divide has grown into a kind of internal war. Another prominent voice inside Iowa's Christian conservative community, Pastor Jamie Johnson, says Cruz has hit a ceiling within the group.

JAMIE JOHNSON, Former Senior Director, Rick Perry for President: It could be his personality, that he naturally seems to rub people the wrong way.

JUDY WOODRUFF:

Johnson, who pastored churches for 25 years, believes Trump could surprise everyone tonight.

JAMIE JOHNSON:

I would say that Iowa's evangelicals are cautious, but excited about the possibility of a President Trump. And they feel that he may have the iron will that is necessary to do a lot of the things that have frustrated Iowa evangelicals and probably evangelicals across the nation for many years now.

JUDY WOODRUFF:

Bob Vander Plaats couldn't disagree more.

BOB VANDER PLAATS:

He's a guy that says he doesn't have to ask God for forgiveness. He's a guy that disparages prisoners of war by saying, "I like veterans who aren't captured." He's a guy who mocks people with disabilities.

DONALD TRUMP (R), Republican Presidential Candidate: My mother gave me this Bible, this very Bible, many years ago.

JUDY WOODRUFF:

Kathedral's Kenney Linhart questions Trump's sincerity.

KENNEY LINHART:

How tattered are the pages of that Bible? And how much of that Bible does he know?

JUDY WOODRUFF:

But Pastor Jamie Johnson argues many Iowa evangelicals are even more focused on finding a strong leader for the country and someone who can win in November.

JAMIE JOHNSON:

I think there's a willingness on the part of many self described born-again Christians that are willing to take a chance on Trump, and pray that God will guide him in a moral and ethical direction.

JUDY WOODRUFF:

Johnson defends Trump's expressions of faith, as do voters like Kathy Simpson, who showed up yesterday to hear Trump speak in Council Bluffs.

KATHY SIMPSON, Trump Supporter:

There are people who don't think Trump is a religious person. I know that he is a religious person.

JUDY WOODRUFF:

Some who belong to Pastor Linhart's church have a different take. Several brought up Trump calling a New Testament book 2 Corinthians.

DONALD TRUMP:

2 Corinthians 3:17, that's the whole ball game.

LIZZIE MONROE, Member, the Kathedral: If he can't pronounce the Bible verse the correct way, it doesn't give me a lot of faith. I mean, my 2-year-old knows how to say a Scripture.

JUDY WOODRUFF:

Brenda McGinnis is enthusiastically for Marco Rubio.

BRENDA MCGINNIS, Rubio Supporter:

I have heard him talk about his salvation. I have heard him use the name of Jesus Christ, which is very important to me.

JUDY WOODRUFF:

Rubio spoke about his faith to a crowd near Des Moines this weekend.

SEN. MARCO RUBIO (R-FL), Republican Presidential Candidate:

You better hope that my that my faith influences me, because I'm a follower of Jesus Christ. And Jesus Christ taught us that, in order to follow him, we have to care and love for one another.

JUDY WOODRUFF:

Pastor Linhart likes what he hears.

KENNEY LINHART:

Marco Rubio has come out so well with his faith so strong, not just said he is a Christian, but that he believes that the word of God should direct his life.

JUDY WOODRUFF:

Whether it's the deciding factor or not in the Republican contest, Pastor Linhart believes it's critical for the Christian community to make its voice heard.

KENNEY LINHART:

As you go about this election cycle tomorrow night, you pray and ask that God shows you the men and women who are subjected to his spirit, because if God is going to change the nation, he's going to do it through human vessels.